Electrical connector



May 7, 1957 K. M. HAMMELL ELECTRICAL CONNECTOR Fiied April 20, 1955 5JM&L 5 m\\ m m 0% l/A% 7/1 2 MH a m mwfi m.

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A vAMI II' ELECTRICAL CONNECTOR Kemper M. Hammell, Harrisburg, Pa.,assignor to AMP Incorporated, a corporation of New Jersey ApplicationApril 20, 1955, Serial No. 502,697

4 Claims. (Cl. 339-258) This invention relates to electrical connectorsand more particularly, in a connector assembly wherein the parts aredesigned for fast and permanent assemblage, to an improved sheet metalreceptacle which grips under spring pressure a mating sheet metal tab. 7

In the art of coupling a pair of conductors with solderless connectorswherein the parts forming the assembly are secured together by thefriction afforded through one part having spring means bearing against asurface on the other part, adequate spring pressure must be provided tosatisfy mechanical requirements, e. g. stability against accidentaldisconnection, while a sufiicient area of electrical contact must alsobe provided to attain the currentcarrying capacity usually desired ofsuch connectors.

The amount of metal in the receptacle available to obtain both themechanical and electrical characteristics desired, however, is limited.It has been the practice, therefore, to concentrate all the availablespring pressure at points or along lines of the tab to achieve a goodmechanical connection, assuming that good electrical characteristicsflow from the high contact pressure thereby obtained.

Reducing the places of contact to lines and points, albeit at highcontact pressure, more or less reduces the current rating of theconnection, but more disadvantageously such contact is highly subject tocorrosion in use even under good conditions, primarily due toaccelerated oxidation caused by the heat inherently generated in theassembly. Thus, although a connection in which reliance is placed online and point contact under high pressure may initially performsatisfactorily even under fairly heavy current loads, such a connectiontends to deteriorate at a fairly high rate and to fall from cor lGSlOIl.

It is, therefore, an object of the present invention to provide anelectrical connector assembly wherein the parts may be quickly assembledin permanent installation yielding a connection which retains highquality mechanical and electrical characteristics throughout the lifeexpectancy of the equipment associated therewith. Another object is toprovide in an electrical connector assembly an improved sheet metalreceptacle for receiving under spring pressure a mating tab. To thesepurposes an optimum area of contact between the elements is providedwithout reducing the contact pressure below the minimum necessary tosecure the assembly from disconnection in normal use whereby, while theperimeter of the contact area may be subject to corrosion, a centralportion of such area will be insulated and protected from corrosivefactors thus assuring an electrical connection of long life and highquality.

Other objects and attainments of the present invention will becomeapparent to those skilled in the art upon a reading of the followingdetailed description when taken in conjunction with the drawings inwhich there is shown and described a preferred embodiment; it is to beunderstood, however, that this embodiment is not intended to beexhaustive or limiting of the invention but is given for purposes ofillustration in order that others skilled in the art may fullyunderstand the invention and the principles thereof and the manner ofapplying it in practical use so that they may modify it in variousforms, each as may be best suited to the conditions of a particular use.

In the drawings:

Figure 1 is a perspective view of the two elements of a connectorassembly illustrating the invention;

Figure 2 is a sectional view of the receptacle elemen taken at line 2-2of Figure 1;

Figure 3 is a sectional view similar to that of Figure 2 but with thetab element in connective relationship with the receptacle element;

Figure 4 is a sectional view taken at line 44 of Figure 3;

Figure 5 is a sectional view taken at line 5-5 of Figure 2; and

Figures 6a to 6d are fragmentary cross-sectional views taken from Figure3 for illustrating certain mechanical deficiencies encountered in theforming process of the connector assembly.

A connector assembly illustrative of the invention includes a tabelement and a receptacle element for receiving and frictionally grippingthe tab, generally designated at 1 and 3 respectively in Figure l, theelements being provided with ferrule means by which each is attached inelectrical connection with the ends respectively of a pair of leads 5 tobe coupled. Typically such ferrule means include barrels 7, each havinga pair of ears 9, curled about and compressed into tight mechanical andelectrical engagement with the hated ends of leads 5 and barrels 11,each having a pair of cars 13 wrapped around and supporting theinsulation of the leads.

The connector elements 1 and 3 may conveniently be fabricatedaccordingto conventional blankingand forming techniques from anysuitable malleable sheet metal stock, such as half to three-quartershard brass, bronze or the like, which will increase in resilience andhardness upon being subjected to a cold-forging or coining operation. Asthus fabricated, in the illustrated embodiment of my invention element 1takes the form of a substantially flat rectangular tab having stopshoulders 15 which engage the front sidewalls of receptacle element 3thereby to define the limit of insertion of the tab within thereceptacle. An indentation or dimple 17 is centrally located on at leastone, and preferably both active surfaces of tab 1 to form with boss 19in receptacle 3 a detent means to be more particularly described.

a To provide for receiving and retaining tab 1 in springlockedelectrical and mechanical engagement, receptacle element 3 includes abase or floor portion 21 from opposed side edges of which extend a pairof flanges 23 having inturned ends 25 overlying and spatially disposedfrom base portion 21, as best shown in Figures 2 to 5. As thus arranged,base portion 21 and flanges 23 define an open-ended channel of slightlygreater width and height than tab 1 which may therein be inserted.Suitably anchored at longitudinally spaced points along base portion 21is a spring 27 in the form of a'flat strip which is bowed out of theplane of base portion 21 and into the channel of the receptacle therebyto bias under pressure tab 1 into engagement with ends 25 of fiange-23.Spring 27 may conveniently be fashioned integrally with base portion 21in the forming operations for the receptacle. To this end a pair ofsubstantially parallel longitudinal: Slts29 cut in base portion 21define the spring strip 27-which thus has -its-ends integral with' base21. Also in the forming operation strip 27 is reduced in thickness ascompared to the original thickness of the sheet metal stock by acold-forging or coining operation where by to impart the desired springcharacteristics thereto, such as hardness-and resilience.

As thus constructed-insertion,oftab 1 inthereceptacle depresses spring27 -which.,bears against the undersurface .of the tab that is intturnsupported by. flange ends 25. A centrally located boss 19,.preferablyraised on the sur- .face of spring 27 during the. coining operationperformed thereon, cooperates with eitheriofindenta-tions 17 .of tab 1to provide a detent which adds to the tensile or pullotf strength of theconnection. It willbexobservedfrom Figures 3 and 4 that in order to beWithdrawnfrorn its connected relationship .with .the receptacle, tab 1must depress spring 27 an amount equal to the height of the .boss abovethe planeof the spring thereby adding to the spring pressure which hasto beovercome. :Boss 19 and indentation 17 may takeany suitablecomplementary form which will mm in the smooth camming of spring 27downwardly upon either insertion or withdrawal of the tab. For example,the boss and indentation may .over boss 19 which thenis freefrorncontact with the tab. -As a result, area contact between-the taband spring surfaces may be achieved, as will be explained. In thisconnection in Figure 3 the undersides 31 of ends 25 are shown in flatabutment in area contact with the upper surface of-tab 1. While this maybe desirable from an electrical conductivity standpoint, such areacontact is extremely difficult-to achieve in practice; surfaces 31 mustbe precisely coplanar while tab 1 must be ab- .solutelyflat and freefrom the edge curvature due to blank- .ing or burrsalong thetab sides asaresult of employing stamping operations in the forming process. Neitherof these conditions can be satisfiedl practically where .blanking andforming processes are employed, hence, in realityonly a line contact on.the tab is obtained with surface 31, various possible conditions beingshown in Figuresfia to 6d, such vcontactbeing unreliable electricallydue-stoits vulnerability to corrosion.

As shown in Figure 5, spring 27 is bowed inwardly of .the receptaclechannel about radii :of curvature R1 at the extremities that aresubstantially less than the radius of curvatureRz of the.centraLportionof the strip to define a central slightly-bowed plateauwhich is flattened, Figure 4, upondepressionof the spring by tab 1.The-central portion of the area of contact thus attained is sufiicientlyisolated from all points which may be attacked by corrosionthat theconnection may support high current loads over a prolonged period. Togain as much area of contact as possible without unduly decreasingcontact pressure, slots '29 should be located as near as possible to-theside edges-of base portion 21, thus increasing the width of the contactarea while adding to the volume of metal comprising the spring.

The primary'conductive path between thetab and receptacle is seen to bethe flattened upper surfaceof spring 27 and the'contacted portion-of theundersur face of the tab. Thus,'spri ng 27 has the dual functionofmechanically'locking, and electrically contactingthe tab. :Mechanically,the spring may vary in form and dimension so longas electricallyanninimum area ofocontact isassured. In this connection the lengthdimension of the contact area is not critical since the minimumrequirements in this respect are usually greatly exceeded. For example,the edge contact illustrated in Figure 6 extends substantially thelength of the tab, but the contact width along the surfaces shown hasbeen found in practice not to exceed 0.015 inch, and usually less, whichis inadequate. Oxide penetrations from both sides of such line contactresults in complete failure of the connection within 500 hours in lifetests simulating actual service by temperature cycling. A contact widthof 0.030 inch, however, has been found to be satisfactory in that theconnection will not fail in temperature cycling until after at least1500 hours time which is the lowest cornmercially acceptable limit.Preferably the contact width is 0060-0080 inch which provides anadequate safety factor and operable time of at least 3500 hours forexceeding in all probability the life of any device utilizing theconnection.

To achieve a contact width of 0060-0080 inch, in view of the small sizefor the receptacle portion of receptacle element 3, typically in the;order of 0.400 inch which may accommodate a spring 0.300 inchin length,the plateau of spring 27 must be nearly flatwith only a slight bow orcrown at radiu R2. ,ln areceptacle of this size a maximum springdeflection.of- 0,.008 inch. will typically accommodate the thickness ofthe tab .and the height of boss 19, but in 0.300 inch this .amountofspring deflection cannot be absorbed by. a springv bowed in accordancewith radius R2 without .beingforced over'center. The radius, ofcurvature R1, at the. spring extremities must be sufiiciently smallerthan radius R2 to raise the nearly flat spring plateau above the planeof fioor 21 far enough to avoid depression of the spring below the planeof the floor, thus effectively increasing the spring length.

Iclaim:

1. An electrical connector for receiving a substantially flatrectangular tab having an indentation in at least one .face comprising abase portion, oppositely disposed side flanges overhanging and formingwith said base portion a receptacle for receiving the tab, a boss onsaid base portion adapted to fit within the indentation to provide adetent for resisting withdrawal of the tab from'the receptacle, saidboss having dimensions smaller than the indentation, relative to thegeneral plane of the contact surfaceslof said base portion and the tabrespectively, so asto be free from forceful engagementwith the tab uponcentering the indentation over said boss.

2. An electrical connector for receiving a substantially flatrectangular tab having an indentation in at least one face comprising abase portion, oppositely disposed side flanges overhanging and formingwith said base portion a a receptacle for receiving the tab, said baseportion including a resilient strip convexly bowed lengthwise of saidreceptacleand adapted to spring-bias-the tab against said flanges and tobe at least partially flattened to provide an area of electrical contactwith the tab, a boss on said member adapted to fit within theindentation to provide a detent obstructing removal of the tab from thcreceptacle, the corresponding dimensions of said boss being smaller thanthe indentation so as to be free from forceful engagement with thetabupon centering the indentation thereover.

3. An electrical connector substantially as set forth in claim 2 whereinsaid strip is defined by two parallel slots in said base portion and isbowed out of the plane of said base portion with radii of curvatureatthe end portions substantially smaller than the radius of curvature ofthe central portion thereof.

4. An electrical connection comprising areceptacle having a baseportionandv opposed side fiangesoverhanging .saidbase portion, saidbase. portion including aresilient ,strip convexly bowed lengthwise ofsaid receptacle, and a substantially fiat tab received within saidreceptacle and spring-biased by said strip against said flanges causingsaid strip to become flattened over a central portion of its length,detent means for resisting removal of said tab including a boss anddimple respectively on said strip and tab within the flattened part ofsaid strip, the corresponding dimensions of said boss being smaller thansaid dimple so as to be free from forceful engagement with the tab.

References Cited in the file of this patent UNITED STATES PATENTSBatcheller May 31, 1949 Batcheller June 10, 1952 Batcheller June 10,1952 Martines Feb. 21, 1956

